Storage system having dynamic volume allocation function

ABSTRACT

An object of the present invention is to allow access to a plurality of logical devices regardless of the number of ports provided in a storage system and the number of logical devices that can be allocated to a single port, and thereby to improve the usability of the logical devices. A storage system comprises a plurality of logical devices, a target device which is the object of access from a computer, and a juke box system for allocating one of the plurality of logical devices to the target device. The juke box system changes the logical device that is allocated to the target device in accordance with a request from the computer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2004-432014, filed on Dec. 26, 2003, the entiredisclosure of which is incorporated herein by reference.

This application also relates to and claims priority from JapanesePatent Application No. 2004-238983, filed on Aug. 19, 2004, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

The present invention relates to a storage system for storing data usedby a computer.

In recent years, the amount of data handled by computers has increaseddramatically, and hence storage devices for storing data are increasingincapacity. At the same time, large storage systems comprising aplurality of disk devices are being designed to store large volumes ofdata in an aggregated fashion, rather than dispersing these largevolumes of data for storage in a large number of small storage devices.

For example, a storage system disclosed in Japanese Unexamined PatentApplication Publication 2003-242039 comprises a plurality of physicaldevices, and manages storage regions constituted by these physicaldevices as logical devices. A host computer connected to the storagesystem can access a logical device by specifying a port ID (a WWN (WorldWide Name) for identifying a port uniquely) and a LUN (Logical UnitNumber) corresponding to the logical device.

Note that hereafter, a device that is specified by a port ID and a LUN,and recognized as a subject of access from a host computer, will bereferred to as a target device.

SUMMARY

There is usually a limit to the number of logical devices that can beallocated to a port of a storage system. Hence, even if the number ofphysical devices provided in a storage system is increased, there arerestrictions on the number of logical devices that can be accessed fromthe host computer.

Hence, a technique is disclosed for improving the usability of a logicaldevice by permitting access to a plurality of logical devices,regardless of the number of ports comprised in a storage system and thenumber of logical devices that can be allocated to a single port.

A storage system comprises plural logical devices, plural targetdevices, each of which is an access target of a computer, and a juke boxsystem which allocates anyone of the plural logical devices to a targetdevice.

The juke box system changes the logical device allocated to the targetdevice in accordance with a command from the computer to a commanddevice, which is one of the plural target devices.

Thus the usability of the logical devices provided in the storage systemcan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a system configuration in a firstembodiment;

FIG. 2 is a view showing a constitutional example of a host computer;

FIG. 3 is a view showing a constitutional example of a storage system;

FIG. 4 is a view showing a constitutional example of a managementdevice;

FIG. 5 is a view showing an example of an access-permitted host list andtarget device-LDEV mapping information;

FIG. 6 is a view showing an example of juke box information;

FIG. 7 is a view showing an example of LDEV information;

FIG. 8 is a view showing an example of definition processing performedby a juke box system;

FIG. 9 is a view showing an example of processing for obtaining storagesystem configuration information from the host computer;

FIG. 10 is a view showing an example of detachment processing;

FIG. 11 is a view showing an example of attachment processing;

FIG. 12 is a view showing an example of reattachment processing;

FIG. 13 is a view showing an example of a system configuration in asecond embodiment;

FIG. 14 is a view showing a constitutional example of a storage systemin the second embodiment;

FIG. 15 is a view showing an example of external storage subsysteminformation;

FIG. 16 is a view showing an example of detachment processing in thesecond embodiment;

FIG. 17 is a view showing an example of attachment processing in thesecond embodiment;

FIG. 18 is a view showing an example of reattachment processing in thesecond embodiment; and

FIG. 19 is a view showing an example of a command issued by the hostcomputer to a command device constituting a juke box system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below using thedrawings. Note that the present invention is not limited to or by theseembodiments.

First Embodiment

(1) System Configuration

FIG. 1 is a view showing one example of the system configuration of thisembodiment.

This system comprises one or more host computers 1, one or more storagesystems 2, and one or more management devices 3. The host computer 1 andstorage system 2 are connected by a first communication path 12,enabling the host computer 1 to perform data input/output processing toand from the storage system 2 via the first communication path 12. Thehost computer 1 and management device 3 are connected by a secondcommunication path 13, and the management device 3 and storage system 2are also connected by the second communication path 13. Thus the hostcomputer 1 is able to perform setting processing on the storage system 2remotely through the second communication path 13 and management device3.

Optical cable, copper wire, or similar is used for the firstcommunication path 12 and second communication path 13. Thecommunication protocols that may be used in the first communication path12 and second communication path 13 include Ethernet, FDDI, FiberChannel, SCSI, Infiniband, TCP/IP, iSCSI, and so on. The communicationprotocols used in the first communication path 12 and secondcommunication path 13 may be the same or different, and there are noparticular limitations thereon.

(2) Host Computer

At least one information processing program (to be referred to hereafteras application program 17 or simply AP 17) is operated on the hostcomputer 1 shown in FIG. 1, and the host computer 1 performsinput/output processing to and from the storage system 2 of the datarequired for the information processing executed by the AP 17.

In this embodiment, a juke box system manager API (ApplicationInterface) 16, a storage system manager 4, and a juke box system manager5 are operated on the host computer 1 as well as the AP 17 in order torealize a juke box function.

The juke box system manager 5 issues commands to the storage system 2 toallocate logical devices (also referred to as LDEV (logical device)hereafter) to the target devices provided in the storage system 2, andto detach the allocation of an LDEV when the LDEV is already allocatedto a target device.

The juke box system manager API 16 mediates between the AP 17 and thejuke box system manager 5 to ensure that the host computer 1 is able touse the juke box function of the storage system 2 in accordance with arequest from the AP 17. In other words, the juke box system manager API16 receives a request from the AP 17 and transmits this request to thejuke box system manager 5. In accordance with the request received fromthe juke box system manager API 16, the juke box system manager 5 issuesa command to the storage system 2 to allocate an LDEV to a target deviceor detach an allocation.

A conceivable example of a case in which the storage system 2 uses thejuke box function in accordance with a request from the AP 17 is whenthe AP 17 is electronic mail software, for example, and received mail isclassified into months and stored in separate LDEVs. To read mailreceived in November, for example, the AP 17 accesses the LDEV storingmail data for November. Then, when the AP 17 wishes to access mailreceived in December, the AP 17 must allocate the LDEV storing mail datafor December to the target device in place of the LDEV storing the maildata for November. At this time, the juke box system manager API 16receives a request to access the mail data for December from the AP 17,and hence instructs the juke box system manager 5 to allocate the LDEVstoring the mail data for December to the target device. On the basis ofthis instruction, the juke box system manager 5 issues a command to thestorage system to change the LDEV that is allocated to the targetdevice.

The storage system manager 4 issues instructions to the storage system 2to obtain configuration information regarding the LDEVs in the storagesystem, indicating whether or not the LDEVs provided in the storagesystem 2 are path-defined to a target device (that is, whether the LDEVsare allocated to a target device) so as to be capable of input/outputprocessing, and so on.

FIG. 2 is a view showing an example of the host computer.

The host computer 1 comprises a CPU (central processing unit) 301,memory 302, a hard disk drive (HDD) 303, a display device 304, an inputdevice 305, an input/output device adapter 307, and a network adapter306. A plurality of each of these components may be provided. The hostcomputer 1 may also comprise a semiconductor memory drive 308, anoptical disk drive 309, a magnetic disk drive 310, and so on.

The HDD stores a program 312 required to operate the host computer (forexample, an OS (operating system)), a juke box system manager program314, a storage system manager program 313, a juke box system manager APIprogram 315, and the AP 17. These programs stored in the HDD 303 arecopied to the memory 302 via a bus 311 when processing is required, andexecuted by the CPU 301. Note that the storage system manager 4, jukebox system manager 5, and juke box system manager API 16 illustrated inFIG. 1 are established when the CPU 301 executes the storage systemmanager program 313, the juke box system manager program 314, and thejuke box system manager API program 315.

The input device 305 is used by a user of the host computer 1 to inputdata or commands into the host computer 1. The input device 305 may be akeyboard or a mouse, for example.

The display device 304 is used to display processing performed by theuser, processing performed by the programs, LDEV configurationinformation obtained by the storage system manager 4, settinginformation, and so on, and therefore a monitor such as a CRT or TFTliquid crystal monitor may be used as the display device 304.

The network adapter 306 is connected to the second communication path 13so that the host computer is able to communicate with the managementdevice 3 via the network adapter 306.

The input/output device adapter 307 is connected to the firstcommunication path 12 so that the host computer is able to perform datainput/output processing to and from the storage system 2 via theinput/output device adapter 307.

(3) Storage System

The storage system 2 shown in FIG. 1 comprises a target device 7, and afirst LDEV 8 and a second LDEV 9 serving as logical devices.

Either the first LDEV 8 or the second LDEV 9 is mapped in the targetdevice 7, and the target device 7 is thus recognized in the hostcomputer 1 as a storage device having the capacity of the mapped LDEV.Once an LDEV has been mapped in the target device 7, the host computer 1can access the LDEV mapped in the target device 7 by accessing thetarget device 7.

The storage system 2 comprises a juke box system 6. The juke box system6 is implemented to realize the juke box function of the storage system2, and realizes a functional interface (I/F) with the host computer. Thejuke box system 6 enables the LDEV allocated to the target deviceprovided in the storage system 2 to be changed in accordance with acommand from the host computer 1.

The juke box system 6 may be implemented according to several methods.For example:

-   1. A dedicated I/F for issuing instructions to the juke box function    of the storage system 2 may be implemented in the host computer so    that the juke box system receives and processes instructions using    this dedicated I/F.-   2. The jukebox system 6 is defined as a special target device    provided in the storage system 2 so that when the host computer    accesses this special target device using a standard I/F, the juke    box system 6 processes instructions from the host computer.

The first method is a realistic method in cases such as when a certaincompany determines the specifications of a command I/F from the hostcomputer to the storage system, for example in a mainframe (MF)computer. The second method is effective in a storage system employingan input/output I/Fused as standard by a large number of vendors, suchas an oft-used SCSI I/F, between the host computer and an externalstorage device of a computer system such as a so-called open system, forexample.

When the second method is used, the juke box system 6 is implemented asa target device recognized by the host computer 1, similarly to thetarget device 7, and serves as a target device used to enable the hostcomputer 1 to instruct the storage system 2 to use the juke boxfunction. When the host computer 1 uses the juke box function of thestorage system 2, the host computer 1 accesses the target device using acommand in which a juke box function command has been attached to astandard read command or write command, and thus instructs control ofthe juke box function.

A device used as a target device when the host computer 1 transmitsvarious commands to the storage system 2 is known as a command device,and an example of such a command device is disclosed in JapaneseUnexamined Patent Application Publication 2002-288108.

Note that in FIG. 1, an example is illustrated in which the storagesystem 2 comprises a single target device and two LDEVs, but the numberof target devices and LDEVs is not limited to the example shown in FIG.1 and any number of target devices and LDEVs may be provided.

FIG. 3 is a view showing an example of the constitution of the storagesystem 2.

The storage system 2 comprises a storage system controller 201 and oneor more physical devices (also referred to as PDEV hereafter) 202. ThePDEV is a physical recording medium such as a hard disk drive, anoptical disk, or tape.

The storage system controller 201 comprises a control processor 203,memory 204, a host adapter 205, a disk adapter 206, and a networkadapter 207.

The host adapter 205 is connected to the host computer 1 via the firstcommunication path 12, and serves as a device for receiving input/outputrequests from the host computer 1 and transmitting appropriate data tothe host computer in accordance with a request from the host computer 1.The host adapter 205 comprises one or more I/O ports (to be referred toas ports hereafter), and each port is identified by a port ID (forexample, a WWN in Fiber Channel). Moreover, one or more target devicescan be accessed from each port. Each target device is identified using aset comprising a port ID (WWN) and a LUN (logical unit number). Notethat in the example in FIG. 3, the storage system 2 is provided with asingle host adapter 205, but the storage system 2 may be provided with aplurality of host adapters 205.

Unless stipulated below, it is assumed that in this embodiment, the I/Oprocessing performed between the host computer and storage systemutilizes Fiber Channel. However, I/O processing may be performedaccording to the communication protocols described above during thedescription of FIG. 1 using a port identifier and identifiers for thedevices that can be accessed from the port. Hence the present inventionis not limited to Fiber Channel.

The disk adapter 206 is used to write data into the PDEV 202 or readdata from the PDEV in accordance with an input/output request from thehost computer 1.

The network adapter 207 is a device for performing communication withthe management device 3 via the second communication path 13.

A host adapter control program 211 for controlling the host adapter, adisk I/O program 212 for controlling the disk adapter, a network controlprogram 213 for controlling the network adapter, a command controlprogram 208 for interpreting commands such as I/O processing requestsfrom the host, a path control program 209 for defining an LDEV as thetarget device 7 (that is, for allocating an LDEV to the target device),a configuration control program 210 for defining the LDEVs in thestorage system 2 and so on, and configuration information 218, which isinformation relating to the LDEVs, PDEVS, and so on in the storagesystem, are stored in the memory 204 for controlling the storage system.

The configuration information 218 comprises target device-LDEV mappinginformation 214 (see FIG. 5), which is created and updated by theconfiguration control program 210, LDEV-PDEV mapping information 215,LDEV information 216 (see FIG. 7), juke box information 217 (see FIG.6), and an access-permitted host list 219 (see FIG. 5).

The LDEVs are storage regions existing in the PDEVs inside the storagesystem 2. The storage system controller 201 manages and controls theLDEVs as logical storage devices. Note that an LDEV may be constitutedby a storage region in a single PDEV, or as a storage region in aplurality of PDEVs. The configuration control program 210 creates theLDEV-PDEV mapping information 215 to define the relationship between theLDEVs and the storage regions within the PDEVs, and manages addresscorrespondence between the LDEVs and PDEVs.

The control processor 203 executes the programs in the memory 204.

(4) Management Device

The management device 3 shown in FIG. 1 comprises a storage systemmanagement mechanism 10 and a storage system management server 11.

The storage system management mechanism 10 sets and holds configurationinformation in the interior of the storage system 2, and obtainsconfiguration information from the storage system 2. The storage systemmanagement mechanism 10 also installs the programs to be operated by thestorage system 2, monitors faults occurring in the interior of thestorage system 2, notifies the user of these faults, and so on.

For example, the storage system management mechanism 10 is capable ofdefining the LDEVs inside the storage system 2, defining paths (that is,allocating an LDEV to the target device), introducing the juke boxsystem into the storage system 2, obtaining definition informationrelating to the LDEVs, paths, and so on from the storage system 2,transmitting definition information to the storage system 2, instructingsetting of the definition information, and so on.

The storage system management server 11 is a mechanism for providing thehost computer with the functions of the storage system managementmechanism 10. For example, the storage system management server 11communicates with a client program operating on a computer such as thehost computer 1 via the second communication path 13, receives requeststransmitted from the client program to the storage system managementmechanism 10, and transfers these requests to the storage systemmanagement mechanism 10. As a result, the storage system managementmechanism 10 is able to perform setting processing on the storage system2, obtain fault information, and so on via the second communication path13 on the basis of requests from the client program.

To configure both the storage system management mechanism 10 and storagesystem management server 11, a program stored in memory provided in themanagement device 3 is executed by a control processor provided in themanagement device 3.

FIG. 4 is a view showing a constitutional example of the managementdevice 3.

The management device 3 is implemented as a computer. The managementdevice 3 comprises a CPU 401, memory 402, an HDD 403, a display device404, an input device 405, and network adapters 406 and 407. Similarly tothe host computer, each of these components may be provided in aplurality. The management device 3 may also comprise a semiconductormemory drive 408, an optical disk drive 409, a magnetic disk drive 410,and so on. These drive devices are used to install programs in thestorage system 2 and management device 3 using appropriate media.

A program required to operate the management device 3 (for example, anOS 412), a storage system management program 413, and a storage systemmanagement server program 414 are stored in the HDD 403. When processingis required, these programs stored in the HDD 403 are copied to thememory 402 via a bus 411 and executed by the CPU 401. When the CPU 401executes the storage system management program 413, the storage systemmanagement mechanism 10 is established, and when the CPU 401 executesthe storage system management server program 414, the storage systemmanagement server 11 is established.

The input device 405 is used by a user of the management device 3 toinput data or commands. The input device 405 may be a keyboard or amouse, for example.

The display device 404 is used to display the processes and results ofprocessing instructed by the user on the management device 3, theprocesses and results of processing executed by the programs, settinginformation, and so on, and therefore a monitor such as a CRT or TFTliquid crystal monitor may be used as the display device 404.

The network adapter 406 is connected to the host computer 1 via thesecond communication path 13. The network adapter 407 is connected tothe storage system 2 via the second communication path 13. Note that thenetwork adapters 406 and 407 may be constituted by the same device.

(5) Configuration Information

Next, the configuration information 218 provided in the storage system 2will be described.

FIG. 5 is a view showing an example of the access-permitted host list219 and target device-LDEV mapping information 214 provided in thestorage system 2.

The access-permitted host list 219 is information in whichidentification information for the target devices that can be accessedby the host computer 1 (i.e. the WWN and LUN serving as theidentification information for the ports) is recorded for each hostcomputer 1 which accesses the storage system 2.

Here, two types of LUN, a host LUN and an internal LUN, exist. The hostLUN is used to enable a host computer to access a target device of thestorage system 2, and the internal LUN is used to enable the storagesystem 2 to identify the target devices provided therein uniquely.

The access-permitted host list 219 comprises a host computer targetdevice list 219(a) in which the target devices that can be accessed by ahost computer are registered for each host computer which accesses thestorage system 2, an in-storage system target device list 219(b) inwhich the target devices existing within the storage system 2 areregistered, and a pointer 219(c) showing the relationship between thesetwo lists.

In the host computer target device list 219(a), host computeridentification information (the WWN of the host computer), and a setcomprising a port ID (WWN) and host LUN used when the host computeraccesses a target device, are registered for each host computer. In thein-storage system target device list 219(b), a set comprising a port ID(WWN) and internal LUN for identifying the target devices provided inthe storage system are registered. The pointer indicates the set of theWWN and internal LUN registered in the in-storage system target devicelist 219(b) to which the set of the WWN and host LUN registered in thehost computer target device list 219(a) corresponds.

In the example in FIG. 5, when a host computer 1A identified by WWNAissues an access request to the storage system 2 specifying WWN=0, hostLUN=0, the storage system 2 is able to determine that the object of theaccess request is the target device identified as WWN=0, internal LUN=0using the access-permitted host list 219. When a host computer 1Bidentified by WWNB issues an access request to the storage system 2specifying WWN=0, host LUN=0, the storage system 2 is able to determinethat the object of the access request is the target device identified asWWN=0, internal LUN=4 using the access-permitted host list 219.

As illustrated above, in some cases the target device to be accessed bythe request source host computer may differ, even when the same WWN=0,host LUN=0 is specified in the access request issued by the hostcomputer. Therefore, the storage system 2 uses the host computeridentification information (the WWN of the host computer) included inthe access request to specify the target device to be accessed.

Also in the example in FIG. 5, a set of a WWN and a host LUN whichcorresponds to the target device identified by WWN=0, internal LUN=4 isnot registered in the target device list 219(a) for the host computer1A. Hence the host computer 1A is unable to access the target deviceidentified by WWN=0, internal LUN=4. By having the storage system 2specify the target device to be accessed using the access-permitted hostlist 219 in this manner, access to a target device from a host computercan be permitted or denied in accordance with the access authority ofeach host computer to access the target devices. More specifically, whenan access request is received from the host computer 1 requesting accessto a target device which the host computer is not permitted to access,the storage system 2 returns an error to the host computer or does notrespond to the request, and is thus able to prohibit access to thetarget device.

The target device-LDEV mapping information 214 shows the LDEVs that arecurrently allocated to the target devices. FIG. 5 shows an example ofthe target device-LDEV mapping information 214 relating to the targetdevice identified by WWN=0, internal LUN=0, but in actuality, one set oftarget device-LDEV mapping information 214 is stored in the memory 204of the storage system 2 for each target device.

The target device-LDEV mapping information is constituted by a pointer1100 for pointing to an entry in the in-storage system target devicelist 219(b) identifying a target device, an LDEV number 1101 whichserves as identification information for the LDEV which corresponds tothe target device (that is, the path-defined LDEV), the condition 1102of the target device, the capacity 1103 of the LDEV corresponding to thetarget device, and a pointer 1104 for pointing to an entry in the jukebox information 217.

The condition 1102 comprises information such as defined/undefined,normal, blocked, whether the target device is a command deviceimplemented as a juke box system, and so on.

FIG. 6 is a view showing an example of the juke box information 217.

The juke box information 217 exists for each LDEV that can be allocated(or in other words path-defined) to each target device. Accordingly,when the storage system 2 is at a maximum, the juke box information 217is provided in a number obtained by multiplying the maximum number ofLDEVs that can be path-defined to each target device by the maximumnumber of implemented target devices. Note that the juke box information217 maybe provided in a queue configuration or the like depending on thecapacity limitations and so on of the control memory, but since thisbears no direct relationship to the essence of the present invention,detailed description is not provided. It goes without saying that othertable configurations are possible as long as all of the LDEVs to be usedin the juke box can be registered for each target device to which thejuke box function is applied.

Note that FIG. 6 shows the juke box information 217 for a single LDEVthat can be path-defined to a certain single target device.

A set 1200 comprising a port ID (WWN) and an internal LUN foridentifying a target device, an LDEV number 1201 for identifying an LDEVthat may be allocated to the target device, a path defining time 1202indicating the time at which the LDEV is allocated to the target device,a path detachment time 1203 indicating the time at which the allocationof the LDEV to the target device is to be detached, a latest access pathdefining time 1204 indicating the time at which the LDEV was allocatedto the target device last, and a latest access path detachment time 1205indicating the time at which the latest allocation of the LDEV to thetarget device is detached are registered in the juke box information217.

Note that the pointer 1104 for pointing to an entry in the juke boxinformation, which is included in the target device-LDEV mappinginformation 214 described above, indicates the top address of the jukebox information 217 of the corresponding target device.

FIG. 7 is a view showing an example of the LDEV information 216.Although FIG. 7 shows the LDEV information 216 of a single LDEV, thestorage system 2 comprises the LDEV information 216 for the maximumnumber of implemented LDEVs.

The LDEV information comprises an LDEV number 1000 serving as an LDEVidentification number, an LDEV condition 1001, a path definition 1002indicating whether or not the LDEV is path-defined, program usageinformation 1003, program reservation information 1004, juke boxinformation 1005, an LDEV capacity 1006, an LDEV emulation type 1007, anLDEV attribute 1008, an attribute setting time 1009 indicating the timeat which the attribute is set, and an attribute modification prohibitionperiod 1010 indicating a period (from the attribute setting time 1009)during which modification of the attribute is prohibited.

The LDEV condition 1001 contains information such as whether the deviceis implemented (defined), whether it is in a normal condition or ablocked condition, whether or not it is serving as a juke box system(i.e. whether the LDEV constitutes a command device serving as a jukebox system as a result of being allocated to a target device), and soon.

In the path definition 1002, if the LDEV is path-defined, a set of aport ID (WWN) and an internal LUN is registered as the identificationinformation of the target device to which the LDEV is allocated, and ifthe LDEV is not path-defined, a null is registered.

The program usage information 1003 indicates whether or not the LDEV isbeing used in a program operated in the interior of the storage system 2(whether or not the LDEV is being used as a juke box system, and whetheror not the LDEV is being used in a program not directly related to thepresent invention (for example, a program for executing processing inthe interior of the storage system to create a replica of the data inthe LDEV in another LDEV, a program for executing processing to copy thedata in the LDEV to an LDEV in another storage system, and so on)), andthe program reservation information 1004 indicates whether or not theLDEV is reserved as an LDEV for use in a program operated in theinterior of the storage system 2.

The juke box information 1005 is a pointer for pointing to the juke boxinformation 217 relating to the LDEV.

The emulation type 1007 is information indicating the emulation type ofthe devices to and from which input and output is possible from the hostcomputer 1, and comprises information such as whether the emulation typeis for an open system host computer, a mainframe host computer, and soon.

The attribute 1008 is information indicating the attribute of the LDEV.Examples of attributes include a read only attribute indicating thatwriting to the LDEV is prohibited, a read/write attribute permittingboth reading of and writing to the LDEV, a protect attribute prohibitingall processing on the LDEV, and an SVOL-disable attribute prohibitinguse of the LDEV as an LDEV for storing a replica of data stored onanother LDEV. Identification information (for example, the WWN of thehost computer 1) for the host computers that are permitted to access theLDEV may also be registered as the attribute 1008.

Note that as the configuration information 218, the storage system 2comprises the LDEV-PDEV mapping information 215 in addition to theinformation illustrated in FIGS. 5 through 7. However, as noted above,the LDEV-PDEV mapping information 215 is information indicating therelationship between the PDEVs and LDEVs, and is not described in detailhere.

(6) Definition Processing for a Command Device Serving as the Juke BoxSystem 6

FIG. 8 is a view showing an example of definition processing for acommand device serving as the juke box system 6, which is executed bythe storage system management program 413 of the management device 3 andthe configuration control program 210 of the storage system 2. A user ofthe juke box system may set the juke box system 6 in the storage system2 via the storage system management program 413 of the management device3.

The user activates the storage system management program 413, whereuponthe storage system management program 413 transmits a configurationinformation acquisition command to the configuration control program 210of the storage system 2 in order to search the configuration information218 of the storage system 2 (step 501). Note that the user is able toinstruct the storage system management program 413 by connecting to thestorage system management server program 414 from the host computer 1via the second communication path 13, and is also able to instruct thestorage system management program 413 using the display device 404 andinput device 405 of the management device 3. The configurationinformation acquisition command is received by the storage system 2 viathe second communication path 13.

Having received the configuration information acquisition command (step502), the configuration control program 210 transmits the configurationinformation 218 of the storage system 2 to the management device 3 (step503).

Having received the configuration information (step 504), the storagesystem management program 413 outputs the received configurationinformation to the display device 404, or transmits the configurationinformation to the host computer 1 used by the user via the storagesystem management server program 414 and second communication path 13.

The user refers to the path definition 1002 of the LDEV information 216in the configuration information output by the management device 3 tosearch the storage system 2 for an LDEV which is not path-defined. Theuser then inputs an instruction to set the found LDEV as a juke boxsystem, specifying the LDEV number of the LDEV. On the basis of thisinstruction, the storage system management program 413 createsdefinition information indicating that the LDEV denoted by the number ofthe received LDEV is set as the juke box system 6 (that is, the targetdevice to which the LDEV corresponds is set as a command device for thejuke box system 6) (step 505). Note that specification of the LDEV tobecome the juke box system may be performed automatically by having thestorage system management program 413 search the path definition 1002 inthe LDEV information 216, rather than by means of an instruction givenby the user.

The storage system management program 413 also transmits a configurationinformation update command to the configuration control program 210 viathe second communication path 13 (step 506).

Having received the configuration information update command (step 507),the configuration control program 210 transmits a configurationinformation update preparation completion response indicating receptionof this command to the storage system management program 413 (step 508).

Having received the response (step 509), the storage system managementprogram 413 transmits the definition information created in step 505 tothe configuration control program 210 via the second communication path13 (step 510).

Having received the definition information (step 511), the configurationcontrol program 210 updates the configuration information according tothe received definition information, thereby defining the LDEV indicatedby the LDEV number specified by the storage system management program413 as the juke box system 6. More specifically, information indicatinga jukebox system is stored in the condition 1001 of the LDEV information216 for the LDEV number specified by the definition information, and theidentification information (port ID (WWN) and internal LUN) of thetarget device used as the command device is stored in the pathdefinition information. Further, the configuration control program 210updates the target device-LDEV mapping information 214 on the basis ofthe received definition information, and relates the command device tothe LDEV specified by the definition information. The configurationcontrol program 210 also updates the juke box information 217 relatingto the LDEV and command device specified by the definition information.The configuration control program 210 then transmits a configurationinformation update completion report to the storage system managementprogram 413 (step 512).

Having received the configuration information update completion report(step 513), the storage system management program 413 outputs an updatecompletion report to the user, whereupon a state of standby is enteredto await confirmation of the end of processing. When an end instructionis input into the management device 3 by the user, the storage systemmanagement program 413 ends the processing (step 514).

(7) Processing for Obtaining the Configuration Information 218 from theHost Computer 1

FIG. 9 is a view showing an example of a processing procedureimplemented when acquiring the configuration information 218 of thestorage system 2 from the host computer 1.

The host computer 1 using the storage system 2 uses the storage systemmanager program 313 to issue a configuration information acquisitionrequest command to the juke box system 6 that has become usable as aresult of the setting processing shown in FIG. 8, and is thus able toobtain the configuration information 218 of the storage system 2. Byobtaining the configuration information 218 of the storage system 2, thehost computer is able to confirm the target devices to which the jukebox function can be applied and the LDEVs that have been newly allocatedto the target devices using the juke box function.

The user activates the storage system manager program 313 on the hostcomputer 1, whereupon the storage system manager program 313 transmits aconfiguration information acquisition request command for searching theconfiguration information of the storage system 2 with the juke boxsystem 6 of the storage system 2 as the target device (or in otherwords, with the command device in which the juke box system 6 isimplemented as the target device) (step 601).

Having received the configuration information acquisition requestcommand over the first communication path 12 (step 602), the storagesystem controller 201 processes the configuration informationacquisition request command received by the command control program 208in a similar manner to the input/output processing performed on a normaltarget device. In other words, the command control program 208interprets the content of the received command, determines that thecommand is a configuration information acquisition request command, andtransmits a configuration information acquisition preparation request tothe configuration control program 210 (step 603). The command controlprogram 208 also transmits a response indicating reception of theconfiguration information acquisition request command to the storagesystem manager program 313 of the host computer 1 (step 606).

Having received the response relating to the configuration informationacquisition request command (step 607), the storage system managerprogram 313 transmits a configuration information acquisition command tothe juke box system 6 (step 608).

Meanwhile, having received the configuration information acquisitionpreparation request from the command control program 208 (step 604), theconfiguration control program 210 prepares the configuration informationfor transmission to the command control program 210 (step 605). At thistime, the configuration control program 210 prepares the LDEVinformation 216 for the LDEVs that can be allocated to the targetdevices corresponding to the content of the host computer target devicelist 219(a) for the host computer 1 which issued the configurationinformation acquisition request command, and the set comprising the WWNand LUN recorded in this host computer target device list 219(a), andthe juke box information 217 relating to these target devices. Thisinformation may be obtained by referring to the access-permitted hostlist 219, the juke box information 217, and the LDEV information 216.

Having received the configuration information acquisition command overthe first communication path 12 (step 609), the command control program208 of the storage system controller 201 analyzes the received command,interprets the command to be a configuration information acquisitioncommand, and transmits a configuration information acquisition requestto the configuration control program 210 (step 610).

Having received the configuration information acquisition request (step611), the configuration control program 210 informs the command controlprogram 208 of the memory address at which the configuration informationprepared in step 605 is stored and the size of the preparedconfiguration information, and transmits a configuration informationpreparation completion report to the command control program (step 612).

Having received the configuration information preparation completionreport from the configuration control program 210 (step 613), thecommand control program 208 reads the configuration information from thememory region indicated by the memory address notified by theconfiguration control program 210, and transmits the configurationinformation to the host computer 1 (step 614).

Having obtained the configuration information from the command controlprogram 208 (step 615), the storage system manager program 313 of thehost computer 1 displays the configuration information to the user onthe display device 304, and then ends configuration informationacquisition processing.

FIG. 19 is a view showing examples of commands issued by the hostcomputer 1 to the storage system 2. Note that identification informationidentifying the host computer 1 (for example, the WWN of the hostcomputer 1), which is the source of the command, is included in thecommands shown in FIG. 19, although not illustrated in FIG. 19 itself.The various commands issued by the host computer 1 to the juke boxsystem (command device) take a read command or write command format toor from the command device, as shown in FIG. 19.

FIG. 19C shows an example of a configuration information acquisitionrequest command 2002 issued by the storage system manager program 313 instep 601. This command takes a read command format. The commandcomprises “JUKE BOX”, indicating that the command is addressed to thecommand device constituting the juke box system, and a port ID (WWN) andhost LUN for identifying a certain target device that can be accessedfrom the host computer 1.

When the identification information of the target device (port ID (WWN)and host LUN) is specified in the configuration information acquisitionrequest command, as shown in FIG. 19C, in step 605 the configurationcontrol program 210 prepares the LDEV information 216 for the LDEVs thatcan be accessed from the target device that is specified by the set ofthe port ID (WWN) and host LUN in the configuration informationacquisition request command 2002 and the identification information ofthe host computer, and the juke box information 217 relating to thetarget device.

Note that identification information for the target device need not beincluded in the configuration information acquisition request command2002. In such a case, as described in step 605 of FIG. 9, a list of thetarget devices that can be accessed from the host computer which is theissuing source of the configuration information acquisition requestcommand 2002, the juke box information 217 relating to each of thetarget devices included in the list, and the LDEV information 216 of theLDEVs that can be allocated to each of the target devices is prepared bythe configuration control program 210.

(8) LDEV Detachment Processing

FIG. 10 is a view showing an example of detachment processing fordetaching a path definition to a target device by disengaging the LDEVallocation to the target device.

The host computer 1 uses the configuration information 218 obtainedthrough the processing shown in FIG. 9, which was performed using thestorage system manager program 313, to perform processing to substitutethe LDEV allocated to a target device using the juke box system managerprogram 314. FIG. 1 illustrates this example. On the basis of a requestfrom the juke box system manager 5 of the host computer 1, the juke boxsystem 6 of the storage system 2 substitutes the first LDEV 8 allocatedto the target device 7 for the second LDEV 9.

First, LDEV detachment (disengagement) processing will be describedusing an example of processing to disengage the first LDEV from thetarget device to which it is allocated.

The juke box system manager program 314 uses the juke box function tohalt input/output processing on the first LDEV to be disengaged from thetarget device (step 701).

The juke box system manager program 314 then halts the input/outputprocessing of the application performing input/output processing on thetarget device to which the first LDEV is allocated, and at the same timetransmits a write command to the storage system to ensure that datawhich were cached in the memory 302 of the host computer 1 during theinput/output processing executed on the target device up to the present,but have not yet been written into the storage system 2, are writteninto the storage system 2.

This write command is received by the command control program 208 of thestorage system 2, whereupon write processing is executed by the disk I/Oprogram 212 (not shown in the drawing).

When the write processing based on the write command is complete, thejuke box system manager program 314 transmits to the juke box system 6(or in other words the command device) a read only attribute assignmentcommand requesting that from now on, only read processing be permittedon the first LDEV to be substituted (step 702). At this time, the jukebox system manager program 314 transmits a port ID (WWN) and host LUN tothe juke box system 6 to specify the target device to which the firstLDEV, which is the object of read only attribute assignment, isallocated.

Having received the read only attribute assignment command (step 703),the command control program 208 interprets the received command, andspecifies the identification number of the first LDEV which is theobject of read only attribute assignment by referring to theaccess-permitted host list 219 and the target device-LDEV mappinginformation 214. The command control program 208 then instructs theconfiguration control program 210 to assign a read only attribute to thespecified first LDEV (step 704).

On the basis of the LDEV number notified in step 704, the configurationcontrol program 210 updates the attribute 1008 of the LDEV information216 corresponding to the LDEV number to a read only attribute (step705). The configuration control program 210 then transmits notificationof the completion of read only attribute assignment to the commandcontrol program 208 (step 706).

Having received this notification of the completion of read onlyattribute assignment (step 707), the command control program 208transmits a read only attribute assignment completion response to thehost computer 1 (step 708).

Having received the read only attribute assignment completion response(step 709), the juke box system manager program 314 in the host computertransmits an LDEV detach command to the juke box system 6. The detachcommand specifies a port ID (WWN) and host LUN serving as theidentifiers of the target device to which the first LDEV to besubstituted is allocated (step 710).

Having received the detach command from the host computer 1, the commandcontrol program 208 interprets the command and transmits a detachmentrequest to the path control program 209 (step 711)

The path control program 209 uses the access-permitted host list 219 tospecify the port ID (WWN) and internal LUN of the target device which isthe subject of the detachment request (step 712). The path controlprogram 209 then checks whether the specified target device isimplemented, whether the target device is faulty, whether the hostcomputer 1 which transmitted the detach command is authorized to accessthe target device, and so on. This information can be confirmed byreferring to the target device-LDEV mapping information 214, theaccess-permitted host list 219, and so on in the configurationinformation 218.

Following this confirmation processing, the path control program 209performs path definition detachment. More specifically, the path controlprogram 209 creates definition information to be notified to theconfiguration control program 210 in order to disengage the first LDEVfrom the target device. The path control program 209 then notifies theconfiguration control program 210 of the path definition modificationand the created definition information (step 713).

Having received this notification (step 714), the configuration controlprogram 210 deletes the target device-LDEV mapping information 214relating the target device to the detached first LDEV on the basis ofthe definition information. The configuration control program 210 alsoupdates the LDEV information 216 of the first LDEV, and registers a nullin the path definition 1002. The configuration control program 210 alsoupdates the jukebox information 217, registers the current time in thelatest access path detachment time 1205, and registers the time that isregistered in the path definition time 1202 in the latest access pathdefinition time 1204. The configuration control program 210 thentransmits a completion report to the path control program 209 (step715).

Having received the completion report from the configuration controlprogram 210, the path control program 209 transmits an LDEV detachmentcompletion response to the command control program 208 (step 716).Having detected the detachment completion response, the command controlprogram 208 transmits a detachment completion response corresponding tothe detach command received in step 710 to the host computer 1 (step717).

Having received the detachment completion response (step 718), the jukebox system manager program 314 outputs completion information to thedisplay device 304, and then ends detachment processing.

Note that the reason for changing the attribute of the first LDEV thatis disengaged from the target device to a read only attribute from step702 to step 709 is that depending on the AP 17 operating on the hostcomputer 1, there may be a desire to change the data in the LDEV that isdisengaged from the target device after the end of writing processing toa WORM (write once read many) format to ensure that the data are notmanipulated. In a case where the AP 17 is mail software, for example,when November moves into December, the LDEV storing the mail data forNovember may be disengaged from the target device and a new LDEV forstoring mail data for December may be allocated to the target device. Byassigning are ad only attribute to the detached LDEV in this case, themail data for November can be protected from further manipulation. Hencewhen an LDEV that is disengaged from a target device following writingprocessing is to be used as a read only archive LDEV, it is preferablethat a read only attribute be assigned to the LDEV prior to detachmentprocessing. If, on the other hand, there is a possibility that rewritingprocessing will be executed on the LDEV that is disengaged from thetarget device following writing processing in the future, the processingof steps 702 through 709 may be omitted.

Note that in the example in FIG. 10, the LDEV is disengaged from thetarget device when the detach command is issued from the host computer1, but the storage system 2 may begin the processing of steps 704through 707 and steps 711 through 717 automatically when the timerecorded in the path detachment time 1203 of the juke box information217 is reached.

FIG. 19D is a view showing an example of a read only attributeassignment command 2003 issued from the juke box system manager program314 in step 702. The read only attribute assignment command 2003comprises “JUKE BOX”, identifying the juke box system (command device)of the command destination, a port ID (WWN) and host LUN specifying thetarget device to which the first LDEV, which is to be assigned with theread only attribute, is allocated (path-defined), and the information“Attribute (Read Only)” indicating that a read only attribute is to beassigned. Note that the read only attribute assignment command 2003takes a write command format.

FIG. 19B is a view showing an example of a detach command 2001 issuedfrom the juke box system manager program 314 in step 710. The detachcommand 2001 comprises “JUKE BOX”, identifying the juke box system ofthe command destination, “Detach Device” indicating that the command isa detach command, a set of a port ID (WWN) and host LUN serving as theidentification information of the target device to which the LDEV to bedetached is path-defined, the LDEV number of the first LDEV to bedetached, information indicating that the detachment subject first LDEVmay be changed to a WORM format as an option, and information indicatingthe time period of the WORM format. Note that as long as the targetdevice subject to detachment can be specified, the LDEV number of theLDEV to be detached need not be included in the detach command.

(9) LDEV Attachment Processing

FIG. 11 is a view showing an example of attachment processing forsetting a path definition to a target device by allocating a new LDEV tothe target device.

LDEV attachment processing will be described using an example in which,following the processing shown in FIG. 10, the juke box function is usedto newly allocate the second LDEV to a target device.

The juke box system manager program 314 transmits to the juke box system6 (or in other words the command device) of the storage system 2 acommand (also referred to as “attach command” hereafter) indicating thatthe second LDEV is to be newly allocated to a target device (step 801).The attach command comprises identification information (i.e. a port ID(WWN) and host LUN) for the target device that is the subject of theattach command, and the LDEV number of the second LDEV to be newlyallocated to the target device.

Having received the attach command (step 802), the command controlprogram 208 analyzes the command to determine that the command relatesto input/output processing on the jukebox system 6 and that the contentof the command is an attachment request to allocate the second LDEV tothe target device, and then transmits an attachment request to the pathcontrol program 209 requesting that the second LDEV be path-defined tothe target device (step 803).

Having received the attachment request, the path control program 209specifies the identifiers (i.e. the port ID (WWN) and internal LUN) ofthe target device that is the subject of the received attachment requeston the basis of the attachment request (step 804). This processing maybe performed by referring to the access-permitted host list 219. Thepath control program 209 also checks whether an LDEV is path defined tothe specified target device. This processing may be performed byreferring to the configuration information 218, and in particular thetarget device-LDEV mapping information 214.

Next, the path control program 209 checks the second LDEV to beallocated to the target device (step 805). More specifically, the pathcontrol program 209 confirms that the LDEV is normal (not faulty), theLDEV is not allocated to other processing, the LDEV is not reserved forother processing, the LDEV is not path defined, the LDEV has not beenallocated to the target device by the juke box system up to the present,and so on. This information can be confirmed by referring to thecondition 1001, program usage information 1003, program reservationinformation 1004, and path definition 1002 in the LDEV information 216of the second LDEV, and the latest access path definition time 1204 inthe juke box information 217.

Next, the path control program 209 allocates the second LDEV to thetarget device specified by the attach command, and path-defines thesecond LDEV to the target device. In other words, the path controlprogram 209 creates definition information for allocating the secondLDEV to the target device. The path control program 209 then transmitsnotification of the new path definition to the configuration controlprogram 210 together with the definition information (step 806).

Having received this notification (step 807), the configuration controlprogram 210 rewrites the target device-LDEV mapping information 214 onthe basis of the received definition information such that the secondLDEV is allocated to the target device that is the subject ofattachment. The configuration control program 210 also modifies the LDEVinformation 216 relating to the second LDEV, and records the port ID(WWN) and internal LUN serving as the identification information of thetarget device to which the second LDEV is allocated in the pathdefinition 1002. Further, the configuration control program 210 updatesthe juke box information 217, and records the current time in the pathdefinition time 1202 and the estimated disengagement time of this pathsetting in the path detachment time (step 808).

The configuration control program 210 then notifies the path controlprogram 209 that update processing of the configuration information 218is complete, and upon reception of this notification, the path controlprogram 209 transmits an attachment completion response to the commandcontrol program 208 (step 809).

Having detected the attachment completion response, the command controlprogram 208 transmits to the host computer 1 an attachment processingcompletion response which serves as a response to the attach commandreceived in step 802 (step 810).

Having received the attachment processing completion response from thestorage system 2 (step 811), the juke box system manager program 314reacknowledges the target device, and if the capacity of the device haschanged, detects this change and confirms the capacity of the new secondLDEV (step 812).

The juke box system manager program 314 then allows I/O processing torecommence on the target device, writes the identification informationof the target device, the identification information of the hostcomputer 1 (or the juke box system manager 5), and the date and time atwhich the path definition was set in a specific region of the newlyallocated LDEV (step 813), and then ends the processing.

By means of the above, attachment processing can be performed toallocate the new second LDEV to the target device. When the hostcomputer 1 places an access request (a read or write request) for accessto the target device to which the second LDEV is newly path definedafter the end of this attachment processing, the storage system 2executes access processing on the second LDEV on the basis of theupdated target device-LDEV mapping information 214.

FIG. 19A is a view showing an example of an attach command 2000 issuedin step 801. The attach command 2000 comprises “JUKE BOX” indicating thedestination of the command, “Attach Device” indicating that the commandis an attach command, a set of the WWN and host LUN serving as theidentification information of the target device that is subject toattachment, and an LDEV number for identifying the LDEV to be attached.

(10) Reattachment Processing for an LDEV that has been Path Defined to aTarget Device in the Past

FIG. 12 shows an example of processing to reattach an LDEV to a targetdevice after being path defined to the target device in the past andthen detached therefrom.

Note that the attachment processing shown in FIG. 11 is performed toallocate a new LDEV to a target device, whereas the reattachmentprocessing shown in FIG. 12 is performed to reattach an LDEV to a targetdevice after having been allocated to the target device once in the-pastand then disengaged therefrom.

Moreover, in cases where the second LDEV is to be path defined to atarget device to which the first LDEV is path defined in place of thefirst LDEV, in FIGS. 10 and 11 the host computer 1 first issues a detachcommand relating to the first LDEV, then executes detachment processingon the storage system 2, then issues an attach command relating to thesecond LDEV, and then executes attachment processing on the storagesystem 2. In the processing shown in FIG. 12, however, detachmentprocessing for the first LDEV and attachment processing for the secondLDEV are executed in the storage system 2 simply by having the hostcomputer 1 issue a single attach command for the second LDEV.

Note that as long as the processing flow shown in FIG. 12 is followed,detachment processing and attachment processing may be executed in thestorage system 2 as a series of processes based on a single attachcommand regardless of whether the LDEV to be attached is a new LDEV oran LDEV that has been attached to a target device once before.

The juke box system manager program 314 transmits to the jukebox system6 (or in other words the command device) an attach command specifying aport ID (WWN) and host LUN set serving as the identification informationof the target device subject to processing, and an LDEV number servingas the identification number of the LDEV to be reattached to the targetdevice (step 901). Note that at this time, the attach commandtransmitted by the juke box system manager program 314 takes the sameformat as the attach command 2000 shown in FIG. 19A.

Having received the attach command (step 902), the command controlprogram 208 transmits an attachment request to the path control program(step 903).

The path control program 209 specifies a port ID (WWN) and internal LUNset serving as the identification information of the target device thatis subject to processing, and determines whether an LDEV is alreadyallocated to the target device by referring to the target device-LDEVmapping information 214 (step 904). At this time, similarly to step 712in FIG. 10, the path control program 209 checks whether the specifiedtarget device is implemented, whether the target device is faulty,whether the host computer 1 which transmitted the attach command isauthorized to access the target device, and so on.

The path control program 209 also confirms the LDEV number of the LDEVthat is currently attached to the target device that is subject toprocessing (step 905). Then, similarly to step 713 in FIG. 10, the pathcontrol program 209 creates definition information to disengage the LDEVspecified in step 905 from the target device specified in step 904 (step906).

Next, on the basis of the-attach command received from the hostcomputer, the path control program 209 confirms the LDEV number of theLDEV to be path defined to the target device specified in step 904 (step907), and checks that the LDEV to be attached is normal (not faulty),the LDEV is not allocated to other processing, the LDEV is not reservedfor other processing, the LDEV is not path defined, and so on.

Next, similarly to step 806 in FIG. 11, the path control program 209creates definition information to path define the LDEV specified in step907 to the target device specified in step 904. The path control program209 then transmits notification that the path definition for the targetdevice specified in step 904 has been modified (i.e. that the LDEV hasbeen substituted) to the configuration control program 210 together withthe definition created in step 906 and step 908 (step 908).

Having received notification of the path definition modification (step909), the configuration control program 210 updates the targetdevice-LDEV mapping information 214, LDEV information 216, and juke boxinformation in accordance with the received definition information (step910). More specifically, the target device-LDEV mapping information 214is updated to relate the LDEV specified in step 907 to the target devicespecified in step 904. Further, the LDEV information 216 for thedetached LDEV specified in step 905 is updated such that a null isinserted in the path definition 1002 of this LDEV, and in the juke boxinformation 217 relating to this LDEV, the time recorded in the pathdefinition time 1202 is registered in the latest access path definitiontime 1204, and the current time is registered in the latest access pathdetachment time 1205. Further, the LDEV information 216 for the attachedLDEV specified in step 907 is updated such that the port ID (WWN) andinternal LUN set specified in step 904 is recorded in the pathdefinition 1002 of this LDEV, and in the juke box information 217relating to this LDEV, the current time is recorded in the pathdefinition time 1202, and the estimated future time at which the LDEV isto be disengaged from the target device is recorded in the pathdetachment time 1203. The configuration control program 210 thennotifies the path control program 209 that modification processing ofthe configuration information is complete.

Having received this completion notification from the configurationcontrol program 210, the path control program 209 transmits anattachment completion response to the command control program 208 (step911).

Having received the attachment completion response from the path controlprogram 209, the command control program 208 transmits to the hostcomputer 1 an attachment completion response which serves as a responseto the attach command received in step 902 (step 912).

Having received the attachment completion response (step 913), similarlyto step 812 in FIG. 11, the jukebox system manager program 314 of thehost computer 1 reacknowledges the target device subject to processingand confirms the modified capacity of the device (step 914). The jukebox system manager program 314 also allows I/O processing to recommenceon the target device, reads the identification information of the targetdevice, the identification information of the host computer (or the jukebox system manager 5), and the date and time of path definition, whichare recorded in a specific region of the reattached LDEV, to confirmthat the reattached LDEV is definitely the LDEV for which reattachmentwas requested by the juke box system manager program 314 in step 901(step 915), and then ends the processing.

Note that the identification information of the target device, theidentification information of the host computer (or the juke box systemmanager 5), and the date and time of path definition, which are readfrom a specific region of the LDEV in step 915, correspond to theinformation that was written into the specific region of the LDEV whenthe LDEV was first attached in step 813 of FIG. 11. The host computer 1stores the information that is written into the LDEV in step 813 of FIG.11, and hence when the LDEV is reattached in step 915, this informationcan be checked to confirm that the attached LDEV is the intended LDEV.

By means of this processing, an LDEV that was attached to a targetdevice once before and then detached therefrom can be reattached to thetarget device and accessed.

Also by means of this processing, an LDEV that is attached to a targetdevice can be exchanged by issuing a single attach command from the hostcomputer 1.

According to the first embodiment described above, an LDEV correspondingto a target device can be altered from a host computer. Hence the hostcomputer can access a plurality of LDEVs using a single target device.As a result, situations in which an LDEV that is rarely accessed remainsallocated to the target device, causing a decrease in the usability ofthe storage system, can be prevented.

Moreover, a read only attribute is attached to an LDEV that is no longerallocated to the target device such that writing to this LDEV isprohibited by the storage system controller, and hence the data storedin the LDEV can be protected from manipulation.

Second Embodiment

(1) System Constitution

FIG. 13 is a view showing an example of the system constitution in asecond embodiment.

The system constitution of the second embodiment differs from the systemconstitution of the first embodiment in that the storage system 2comprises an external storage connection mechanism 24, and the storagesystem 2 is connected to another storage system (second storage system)20 via this external storage connection mechanism 24. Otherwise, thesystem constitution of the second embodiment is identical to that of thefirst embodiment.

The external storage connection mechanism 24 connects to the secondstorage system 20 in order to execute processing to provide the hostcomputer 1 with the target devices of the second storage system 20 (thetarget devices of the second storage system 20 will also be referred toas LUs (logical units) hereafter) as the LDEVs of the storage system 2.More specifically, when the host computer 1 issues an I/O request to atarget device attached with an LDEV of the storage system 2, theexternal storage connection mechanism 24 specifies a LU of the secondstorage system 20 which corresponds to the LDEV attached to the targetdevice that is the subject of the I/O request, generates an I/O requestaddressed to this LU (in other words, an I/O request specifying the WWNand host LUN of the LU), and issues the request to the second storagesystem 20. In so doing, the external storage connection mechanism 24transfers the I/O request from the host computer 1 to the second storagesystem 20 while concealing the existence of the second storage system 20from the host computer 1.

The juke box system 6 in the second embodiment not only executesprocessing to exchange the LDEVs allocated to the target device 7 of thestorage system 2, but also executes processing to exchange the LUS ofthe second storage system 20 corresponding to the LDEVs of the storagesystem 2.

(2) Storage System

FIG. 14 is a view showing an example of the constitution of the storagesystem 2 in the second embodiment.

The second embodiment differs from the first embodiment in that thestorage system 2 comprises an external storage subsystem adapter 2302serving as an adapter for connecting to the second storage system 20, anexternal storage subsystem connection program 2301 for executingprocessing to transmit an I/O request to the second storage system 20 onthe basis of an I/O request received from the host computer 1, andexternal storage subsystem information 2303, which is informationrelating to the LUs of the second storage system 20, which correspond tothe LDEVs in the storage system 2. Otherwise, the constitution of thestorage system 2 of the second embodiment is identical to that of thefirst embodiment.

Note that the constitutions of the host computer 1 and management device3 are identical to those of the first embodiment.

The second storage system 20 is constituted similarly to the storagesystem 2 in the first embodiment. Note, however, that the second storagesystem 20 need not comprise the juke box system 6, and hence in thiscase, the second storage system 20 need not comprise the juke boxinformation 217. In the second embodiment, the host adapter of thesecond storage system 20 and the external storage subsystem adapter 2302of the storage system 2 are connected via a network.

(3) Configuration Information 218

The configuration information 218 provided in the storage system 2 inthe second embodiment is similar to that of the first embodiment exceptfor the LDEV information 216 and external storage subsystem information2303.

The LDEV information 216 in the second embodiment comprises a pointer1011 to the external storage subsystem information in addition to theLDEV information 216 of the first embodiment shown in FIG. 7. When a LUof the second storage system 20 is allocated to the LDEV indicated bythe LDEV information, the storage position in the memory 204 of theexternal storage subsystem information 2303 relating to this LU isregistered in the section for the pointer 1011 to the external storagesubsystem information. When no LU of the second storage system 20 isallocated to the LDEV, a null value is registered.

FIG. 15 is a view showing an example of the external storage subsysteminformation 2303. The external storage subsystem information 2303 shownin FIG. 15 relates to a LU of the second storage system 20 which iscapable of being the destination of an I/O request issued by theexternal storage connection mechanism 24 of the storage system 2 on thebasis of an I/O request from the host computer 1. In actuality, thestorage system 2 comprises the external storage subsystem information2303 for the maximum number of LUs of the second storage system 20 thatcan be supported by the storage system 2.

An ID 1900 of the external storage subsystem LU serves as identificationinformation for identifying a LU of the second storage system 20. Morespecifically, the ID 1900 is a set comprising a port ID (WWN) and hostLUN of the second storage system 20 for identifying the LU. A usage portnumber 1901 is the port ID (in other words, the identification number ofa port provided in the storage system 2) of the target device in thestorage system 2 to which the LDEV of the storage system 2 correspondingto the LU is path defined. A LINK condition 1901 is informationindicating whether the LINK between the LU and the port of the storagesystem 2 is ON or OFF.

A capacity 1902 is the capacity of the LDEV of the second storage system20 which is allocated to the LU. A mapping destination LDEV number 1903is the identification number of the LDEV in the storage system 2 towhich the LU corresponds. A device condition 1904 is informationexpressing the device condition of the LU, in which Not Ready isregistered to indicate that the LU is not path defined, Blockade isregistered to indicate a blocked condition, Formatting is registered toindicate that formatting is underway, Normal is registered to indicate anormal condition, and so on, for example.

A connection definition setting time 1905 is information indicating thetime at which the LU is allocated to the LDEV of the storage system 2specified by the mapping destination LDEV number 1903. A connectiondefinition detachment setting time 1906 is information indicating theestimated time at which the relationship between the LU and the LDEVspecified by the mapping destination LDEV number 1903 is to be detached.A latest connection definition setting time 1907 is informationindicating the time at which the LU was previously allocated to an LDEVof the storage system 2, and a latest connection definition detachmenttime 1908 is information indicating the time at which a previousrelationship between the LU and the LDEV of the storage system 2 wasdetached. A previous mapping LDEV number 1912 is the LDEV number of theLDEV of the storage system 2 to which the LU was previously allocated,and a previous connection port number 1913 is the port ID (that is,identification information for a port of the storage system 2) of theport in the storage system 2 which was used when the LU was previouslyallocated to the LDEV of the storage system 2.

An attribute 1909 is the attribute of the LDEV of the second storagesystem 20 that is path defined to the LU, and similarly to the attribute1008 in the LDEV information 216 shown in FIG. 7, attribute typesinclude read/write, read only, protect, SVOL-disable, and so on. Anattribute setting time 1910 is information indicating the time at whichthe attribute 1909 is set, and an attribute modification prohibitionperiod 1911 is information indicating a time period from the attributesetting time 1910 during which modification of the attribute set in theattribute 1909 section is prohibited.

(4) Processing to Obtain the Configuration Information 218 from the HostComputer 1

In the second embodiment, processing to obtain the configurationinformation 218 through the host computer 1 is similar to the processingof the first embodiment shown in FIG. 9. Note, however, that in step605, the information prepared by the configuration control program 210further comprises the external storage subsystem information 2303relating to the LUs of the second storage system 20 that may beallocated to LDEVs which may be attached to a target device that isaccessible from the host computer.

(5) Detachment Processing

The host computer 1 is capable of using the configuration information218 obtained by the processing shown in FIG. 9, which was performedusing the storage system manager program 313, to exchange a LU of thesecond storage system 20 corresponding to an LDEV using the juke boxsystem manager program 314.

FIG. 13 shows an example of this processing in which the juke box system6 is capable of relating a second external LU 22 of the second storagesystem to the first LDEV 8, which is path defined to the target device7, in place of a first external LU 21 of the second storage systemcorresponding to the first LDEV 8.

First, detachment processing will be described using an example of acase in which the allocation of the first external LU 21 to the firstLDEV is disengaged.

FIG. 16 is a view showing an example of detachment processing fordisengaging a LU of the second storage system 20, which is allocated toan LDEV that is path defined to the target device of the storage system2, from the storage system 2.

The juke box system manager program 314 halts input/output processing onthe first LDEV (step 1601). More specifically, the juke box systemmanager program 314 halts the input/output processing of the applicationwhich performs input/output processing on the target device to which thefirst LDEV is allocated, and at the same time transmits a write commandto the storage system to ensure that data which have been cached in thememory 302 of the host computer 1 during the input/output processingexecuted on the target device up to the present, but have not yet beenwritten into the storage system 2, are written into the storage system2.

This write command is received by the command control program 208 of thestorage system 2, whereupon write processing is executed by the externalstorage subsystem connection program 2301 to write these data into thefirst LU of the second storage system 20 which is allocated to the firstLDEV (not shown in the drawing).

When the write processing based on this write command is complete, thejuke box system manager program 314 transmits to the juke box system 6(or in other words the command device) a read only attribute assignmentcommand requesting that from now on, only read processing be permittedon the first LU (step 1602). Here, the read only attribute assignmentcommand issued by the juke box system manager program 314 takes theformat shown in FIG. 19D. In other words, the read only attributeassignment command 2003 comprises a set of a port ID (WWN) and a hostLUN of the storage system 2 specifying the target device that is pathdefined with the first LDEV to which the subject first LU is allocated.

Having received the read only attribute assignment command (step 1603),the command control program 208 interprets the received command, andspecifies the identification information (i.e. the port ID (WWN) andhost LUN of the storage system 2) of the first LU which is the object ofread only attribute assignment by referring to the access-permitted hostlist 219, the target device-LDEV mapping information 214, the LDEVinformation 216, and the external storage subsystem information 2303.The command control program 208 then instructs the external storagesubsystem connection program 2301 to assign a read only attribute to thespecified first LU (step 1604).

On the basis of the WWN and host LUN serving as the identificationinformation notified in step 1604, the external storage subsystemconnection program 2301 updates the attribute 1909 of the externalstorage subsystem information 2303 corresponding to the WWN and host LUNto a read only attribute (step 1605). Further, the current time is setin the attribute setting time 1910, and the period specified by the readonly attribute assignment command is set in the attribute modificationprohibition period 1911. The external storage subsystem connectionprogram 2301 then transmits notification of the completion of read onlyattribute assignment to the command control program 208 (step 1606).

Having received this notification of the completion of read onlyattribute assignment, the command control program 208 transmits a readonly attribute assignment completion response to the host computer 1(step 1607).

Having received the read only attribute assignment completion response(step 1608), the juke box system manager program 314 in the hostcomputer transmits a detach command to the jukebox system 6 (step 1609).The detach command specifies the port ID (WWN) and host LUN set of thestorage system 2, which serve as identification information for thetarget device that is subject to processing, the LDEV number of thefirst LDEV that is subject to processing, and the port ID (WWN) and hostLUN of the second storage system 20, which serve as identificationinformation for the first LU that is subject to processing.

Having received the detach command from the host computer 1, the commandcontrol program 208 analyzes the command and transmits a detachmentrequest to the path control program 209 (step 1610).

The path control program 209 uses the access-permitted host list 219 tospecify the WWN and internal LUN of the target device which is thesubject of the detachment request (step 1611). The path control program209 then checks whether the specified target device is implemented,whether the target device is faulty, whether the host computer 1 whichtransmitted the detach command is authorized to access the targetdevice, and so on. This information can be confirmed by referring to thetarget device-LDEV mapping information 214, the access-permitted hostlist 219, and so on in the configuration information 218.

The path control program 209 also specifies the first LDEV which is thesubject of the detachment request, and confirms that this LDEV is pathdefined to the target device specified in step 1611 (step 1612).

The path control program 209 also specifies the first LU to be detachedby referring to the LDEV information 216 and external storage subsysteminformation 2303, and confirms that this first LU is allocated to thefirst LDEV specified in step 1612 (step 1613).

Following this confirmation processing, the path control program 209creates definition information for disengaging the path definitionbetween the first LDEV and the first LU, and notifies the configurationcontrol program 210 of the disengagement of the path definition togetherwith the created definition information (step 1614).

Having received this notification (step 1615), the configuration controlprogram 210 rewrites the LDEV information 216 relating to the firstLDEV, and registers a null in the section for the pointer 1011 to theexternal storage subsystem information (step 1616). The configurationcontrol program 210 then notifies the path control program 209 that theLDEV information update is complete.

Having received notification of the completion of the LDEV informationupdate from the configuration control program 210 (step 1617), the pathcontrol program 209 instructs the external storage subsystem connectionprogram 2301 to disengage the path definition between the first LDEV andthe first LU (step 1618).

Having received this instruction from the path control program 209, theexternal storage subsystem connection program 2301 disengages the pathdefinition between the first LU and first LDEV (step 1619). Morespecifically, the external storage subsystem connection program 2301updates the external storage subsystem information 2303 relating to thefirst LU, sets the LINK condition 1901 to OFF, records the valueregistered in the connection definition setting time 1905 in the latestconnection definition setting time 1907, records the current time in thelatest connection definition detachment time 1908, records the LDEVnumber of the first LDEV, which is registered in the mapping destinationLDEV number 1903, in the previous mapping LDEV number 1912, and recordsthe port number registered in the usage port number 1901 in the previousconnection port number 1913 (step 1620). The external storage subsystemconnection program 2301 then transmits a detachment completion responseto the path control program 209.

Having received the detachment completion response from the externalstorage subsystem connection program 2301, the path control program 209transmits a detachment completion response to the command controlprogram 208 (step 1621).

Having detected the detachment completion response, the command controlprogram 208 transmits a detachment completion response to the hostcomputer 1 (step 1622).

Having received the detachment completion response (step 1623), the jukebox system manager program 314 outputs the completed information to thedisplay device 304, and ends detachment processing.

Note that similarly to the first embodiment, the read only attributeassignment processing from step 1602 to step 1608 may be omitted incertain cases.

Furthermore, in the example in FIG. 16 the first LU is disengaged fromthe first LDEV when the detach command is issued from the host computer1, but the processing from step 1604 to step 1607 and from step 1610 tostep 1622 may be executed automatically in the storage system 2 when theconnection definition detachment setting time 1906 of the externalstorage subsystem information 2303 is reached.

FIG. 19F is a view showing an example of the detach command that isissued in step 1609. The detach command comprises “JUKE BOX”, indicatingthe juke box system (command device) that is the destination of thecommand, “Detach Device”, indicating that the command is a detachcommand, a port ID (WWN) and host LUN serving as the identificationinformation of the target device subject to detachment, an LDEV numberindicating the first LDEV subject to detachment, a port ID (WWN) andhost LUN serving as the identification information of the LU in thesecond storage system 20 which is attached to the first LDEV, andinformation indicating that the LU may be set in a WORM format as anoption, and specifying the time period for setting the LU in a WORMformat. Note that the External Dev ( . . . ) section of the detachcommand denotes that the detachment subject is a LU of the secondstorage device 20.

(6) LDEV Attachment Processing

FIG. 17 is a view showing an example of attachment processing for newlyallocating the second LU to the first LDEV in order to set a pathdefinition to the second LU of the second storage system 20 from thetarget device of the storage system 2 via the first LDEV.

Attachment processing will be described using an example in which,following the processing shown in FIG. 16, the juke box function is usedto newly allocate the second LU of the second storage system 20 to thefirst LDEV, which is path-defined to the target device.

The juke box system manager program 314 transmits an attach command tothe juke box system 6 of the storage system 2 (in other words to thecommand device) indicating that the second LU of the second storagesystem 20 is to be allocated to the first LDEV (step 1701). The attachcommand comprises identification information (i.e. a set of the port ID(WWN) and host LUN of the storage system 2) for the target device whichis the subject of the attach command, the LDEV number of the first LDEVallocated to the target device, and identification information (i.e. aset of a port ID (WWN) and host LUN of the second storage system 20) forthe second LU of the second storage system 20 to be newly allocated tothe first LDEV.

Having received the attach command, the command control program 208analyzes the command to determine that the command relates toinput/output processing on the juke box system 6 and that the content ofthe command is an attachment request to allocate the second LU of thesecond storage system 20 to the first LDEV, and then transmits anattachment request to the path control program 209 requesting that thesecond LU of the second storage system 20 be allocated to the first LDEV(step 1702).

Having received the attachment request, the path control program 209specifies the identifiers (i.e. a port ID (WWN) and internal LUN of thestorage system 2) of the target device that is the subject of thereceived attachment request on the basis of the attachment request (step1703). This processing may be performed by referring to theaccess-permitted host list 219.

Next, the path control program 209 specifies the first LDEV which is thesubject of the attachment request (step 1704). The path control program209 then confirms that the specified first LDEV is path defined to thetarget device specified in step 1703, and that the LU of the secondstorage system 20 is not path defined to the specified LDEV. Thisprocessing may be performed by referring to the configurationinformation 218, and particularly the target device-LDEV mappinginformation 214 and LDEV information 216.

The path control program 209 also specifies the second LU of the secondstorage system 20 that is the subject of the attachment request (step1705). The path control program 209 then confirms that the second LU isin a normal condition (not faulty), the LU is not path defined to thetarget device of the storage system 2, the LU has not been allocated tothe target device by the juke box system up to the present, and so on.This information can be confirmed by referring to the device condition1904, usage port number/LINK condition 1901, mapping destination LDEVnumber 1903, and latest connection definition setting time 1907 in theexternal storage subsystem information 2303.

Next, the path control program 209 creates definition information forallocating the second LU of the second storage system 20 to the firstLDEV specified by the attach command, and transmits notification of thepath definition to the configuration control program 210 together withthe definition information (step 1706).

Having received this notification (step 1707), the configuration controlprogram 210 updates the LDEV information 216 relating to the first LDEVon the basis of the received definition information, and records thestorage position in the memory 204 of the external storage subsysteminformation 2303 relating to the first LU in the pointer 1011 to theexternal storage subsystem information (step 1708). The configurationcontrol program 210 then notifies the path control program 209 thatupdating of the LDEV information 216 is complete.

Having received notification of the completion of the LDEV informationupdate from the configuration control program 210 (step 1709), the pathcontrol program 209 instructs the external storage subsystem connectionprogram 2301 to path define the second LU of the second storage system20 to the first LDEV (step 1710).

Having received this instruction, the external storage subsystemconnection program 2301 allocates the second LU of the second storagesystem 20 to the first LDEV (step 1711), and updates the externalstorage subsystem information 2303 relating to the second LU (step1712). More specifically, in the external storage subsystem information2303 relating to the second LU, the port ID (WWN) of the storage system2 specified in step 1703 is recorded in the usage port number 1901, andthe LINK condition 1901 is set to ON. Further, the LDEV number of thefirst LDEV specified in step 1704 is set in the mapping destination LDEVnumber 1903, the current time is set in the connection definitionsetting time 1905, and the time specified in the attach command is setin the connection definition detachment setting time 1906. The externalstorage subsystem connection program 2301 then notifies the path controlprogram 209 of the completion of attachment.

Having received this notification from the external storage subsystemconnection program 2301, the path control program 209 transmits anattachment completion response to the command control program 208 (step1713), whereupon the command control program 208 transmits an attachmentcompletion response to the host computer 1 (step 1714).

When the host computer 1 receives the attachment completion response(step 1715), the juke box system manager program 314 reacknowledges thetarget device, and if the capacity of the device has altered, detectsthis and confirms the capacity of the new second LU. The juke box systemmanager program 314 then allows I/O processing to recommence on thetarget device, writes the identification information of the targetdevice, the identification information of the host computer 1 (or thejuke box system manager 5), and the date and time at which the pathdefinition was set in a specific region of the newly allocated secondLU, and then ends the processing.

By means of the processing described above, attachment processing can beperformed to allocate the new second LU to the first LDEV that isattached to the target device of the storage system 2.

FIG. 19E is a view showing an example of the attach command that isissued in step 1701. The attach command comprises “JUKE BOX”, indicatingthe juke box system that is the destination of the command, “AttachDevice”, indicating that the command is an attach command, a port ID(WWN) and host LUN of the storage system 2 serving as the identificationinformation of the target device subject to attachment, the LDEV numberof the first LDEV allocated to the target device, and a port ID (WWN)and host LUN of the second storage system 20 serving as theidentification information of the second LU of the second storage system20 which is to be newly allocated to the first LDEV. Note that theExternal Dev ( . . . ) section denotes that the device subject toattachment is a LU of the second storage device 20, similarly to thedetach command described above.

(7) Reattachment Processing for a LU of the Second Storage System 20that has been Path Defined to an LDEV of the Storage System 2 in thePast

FIG. 18 is a view showing an example of processing to reallocate a LU ofthe second storage system 20 to an LDEV of the storage system 2 afterhaving been path defined to the LDEV of the storage system 2 in the pastand then detached therefrom.

Note that the attachment processing shown in FIG. 17 is performed toallocate a new LU to an LDEV of the storage system 2, whereas thereattachment processing shown in FIG. 18 is performed to reattach a LUto an LDEV of the storage system 2 after having been allocated to theLDEV once in the past and then disengaged therefrom.

Furthermore, in cases where a LU that is path defined to the first LDEVis to be substituted for another LU, in FIGS. 16 and 17 the hostcomputer 1 first issues a detach command relating to the first LU, thenexecutes detachment processing on the storage system 2, then issues anattach command relating to the second LU, and then executes attachmentprocessing on the storage system 2. In the processing shown in FIG. 18,however, detachment processing for the first LU and attachmentprocessing for the second LU are executed in the storage system 2 simplyby having the host computer 1 issue a single attach command relating tothe second LU.

Note that detachment processing and attachment processing may beexecuted in the storage system 2 as a series of processes based on asingle attach command regardless of whether the LU to be attached is anew LU or a LU that has been attached to an LDEV of the storage system 2once before.

The juke box system manager program 314 transmits to the juke box system6 (or in other words the command device) an attach command (step 1801).The attach command comprises identification information (a port ID (WWN)and host LUN set of the storage system 2) for the target device which isthe subject of the attach command, the LDEV number of the LDEV allocatedto the target device, and identification information (a port ID (WWN)and host LUN set of the second storage system 20) for the LU of thesecond storage system 20 that is to be reattached to the LDEV.

Having received the attach command, the command control program 208interprets the command to be an attach command, and transmits anattachment request to the path control program (step 1802).

The path control program 209 specifies a port ID (WWN) and internal LUNof the storage system 2 serving as the identification information of thetarget device subject to processing (step 1803). This processing may beperformed by referring to the access-permitted host list 219.

Next, the path control program 209 specifies the LDEV subject toprocessing (step 1804), and confirms that the specified LDEV ispath-defined to the target device specified in step 1803. Thisprocessing may be performed by referring to the target device-LDEVmapping information 214.

The path control program 209 also specifies the LU of the second storagesystem 20 that is path defined to the LDEV specified in step 1804, andhence is the subject of detachment. The path control program 209 alsospecifies the LU of the second storage system 20 that is to be newlypath defined to the LDEV, and hence is the subject of attachment (step1805). At this time, the path control program 209 confirms that the LUto be attached is normal, not path defined to an LDEV of the storagesystem 2, and so on.

Following this confirmation processing, the path control program 209detaches the path definition between the LDEV specified in step 1804 andthe detachment subject LU specified in step 1805, creates definitioninformation indicating that the attachment subject LU specified in step1805 has been newly path defined, and transmits this definitioninformation to the configuration control program 210 together withnotification of the path definition setting modification (step 1806).

Having received this notification (step 1807), the configuration controlprogram 210 updates the LDEV information 216 for the detachment subjectLDEV and the attachment subject LDEV on the basis of the receiveddefinition information (step 1808), and notifies the path controlprogram 209 of the completion of the LDEV information update.

Having received this notification (step 1809), the path control program209 instructs the external storage subsystem connection program 2301 tomodify the path definition setting (step 1810).

Having received this instruction, the external storage subsystemconnection program 2301 detaches the path definition of the detachmentsubject LU specified in step 1805 to the LDEV specified in step 1804(step 1811), and path-defines the attachment subject LU specified instep 1805 to the LDEV (step 1812). The external storage subsystemconnection program 2301 then updates the external storage subsysteminformation 2303 in accordance with the path definition settingmodification (step 1813). The content of the modification is similar tothe detachment processing and attachment processing shown in FIGS. 16and 17, and therefore not described in detail here. When the update ofthe external storage subsystem information 2303 is complete, theexternal storage subsystem connection program 2301 transmits anattachment completion response to the path control program 209.

Having received the attachment completion response, the path controlprogram 209 transmits an attachment completion response to the commandcontrol program 208 (step 1814).

Having received the attachment completion response from the path controlprogram 209, the command control program 208 transmits an attachmentcompletion response to the host computer 1 (step 1815).

When the host computer 1 receives the attachment completion response(step 1816), the juke box system manager program 314 reacknowledges thetarget device, and if the capacity of the device has changed, detectsthis and confirms the capacity of the attached LU. The juke box systemmanager program 314 then allows I/O processing to recommence on thetarget device, reads the identification information of the targetdevice, the identification information of the host computer (or the jukebox system manager 5), and the date and time of path definition from aspecific region of the attached. LU to confirm that the attachmentsubject LU is definitely attached (step 1817), and then ends theprocessing.

1. A storage system accessed from a computer, comprising: plural logicaldevices; plural target devices, each of which is an access target of acomputer; and a juke box system which allocates any one of the plurallogical devices to a target device, wherein the juke box system changesthe logical device allocated to the target device in accordance with acommand from the computer to a command device which is one of the pluraltarget devices.
 2. A storage system according to claim 1, wherein thejukebox system changes the logical device allocated to the target devicein accordance with an input/output command from the computer to thecommand device.
 3. A storage system according to claim 2, wherein theinput/output command from the computer to the command device comprisesidentification information for the target device, and the juke boxsystem changes the logical device allocated to the target devicespecified by the input/output command.
 4. A storage system according toclaim 3, further comprising: relationship information betweenidentification information for the computer which accesses the storagesystem and identification information for the target devices which canbe accessed from the computer, wherein the input/output command furthercomprises identification information for the computer which issues theinput/output command, and when the computer specified by theinput/output command is permitted to access the target device specifiedby the input/output command, the jukebox system changes the logicaldevice allocated to the target device on the basis of this relationshipinformation.
 5. A storage system according to claim 2, furthercomprising: target device-logical device mapping information for each ofthe plural target devices, providing identification information for thelogical device that is allocated to each of the target devices, wherein,upon reception of an input/output command from the computer relating toa target device, the storage system executes processing on the logicaldevice allocated to this target device in accordance with the receivedinput/output command on the basis of the target device-logical devicemapping information, and the juke box system changes the logical deviceallocated to the target device in accordance with the input/outputcommand transmitted from the computer to the command device, and updatesthe target device-logical device mapping information in accordance withthe change.
 6. A storage system according to claim 2, wherein theinput/output command issued from the computer to the command devicecomprises a detach command, and the juke box system detaches theallocation of the logical device to the target device specified in thedetach command on the basis of the detach command received from thecomputer.
 7. A storage system according to claim 6, wherein theinput/output command issued from the computer to the command devicecomprises a read only attribute assignment command, the juke box systemassigns a read only attribute to the logical device allocated to thetarget device specified by the read only attribute assignment command onthe basis of the read only attribute assignment command received fromthe computer, and after assigning the read only attribute to the logicaldevice, the juke box system detaches the allocation of the logicaldevice to the target device.
 8. A storage system according to claim 7,wherein both the detach command and the read only attribute assignmentcommand take the format of a write command to the command device.
 9. Astorage system according to claim 2, wherein the input/output commandissued from the computer to the command device comprises an attachcommand, and on the basis of the attach command received from thecomputer, the juke box system allocates the logical device specified inthe attach command to the target device specified in the attach command.10. A storage system according to claim 9, wherein the attach commandtakes the format of a write command to the command device.
 11. A storagesystem accessed from a computer, comprising: a first target deviceserving as the object of access from the computer; a command devicewhich is a second target device serving as the object of access from thecomputer; a logical device allocated to the first target device; anexternal storage connection mechanism connected to another storagesystem which allocates the logical device to a target device of theother storage system; and a juke box system, wherein the jukebox systemchanges the target device of the other storage system, which isallocated to the logical device, in accordance with a command from thecomputer to the command device.
 12. A storage system according to claim11, wherein the external storage connection mechanism transmits aninput/output command to the target device of the other storage system,which is allocated to the logical device allocated to the first targetdevice, in accordance with an input/output command from the hostcomputer addressed to the first target device.
 13. A storage systemaccording to claim 12, further comprising identification information forthe computers which are permitted to access the first target device,wherein the command to the command device comprises identificationinformation for the computer which issues the command, and when thecomputer specified by the command is permitted to access the firsttarget device, the jukebox system changes the target device of the otherstorage system, which is allocated to the logical device allocated tothe first target device, on the basis of the identification informationfor the computer.
 14. A storage system according to claim 12, whereinthe command issued from the computer to the command device comprises adetach command, and on the basis of the detach command received from thecomputer, the juke box system detaches the allocation of the targetdevice of the other storage system to the logical device allocated tothe first target device specified in the detach command.
 15. A storagesystem according to claim 14, wherein the command issued from thecomputer to the command device comprises a read only attributeassignment command, the juke box system assigns a read only attribute tothe target device of the other storage system, which is allocated to thelogical device allocated to the first target device specified by theread only attribute assignment command, on the basis of the read onlyattribute assignment command received from the computer, and afterassigning the read only attribute, the juke box system detaches theallocation of the target device of the other storage system to thelogical device.
 16. A storage system according to claim 12, wherein thecommand issued from the computer to the command device comprises anattach command, and on the basis of the attach command received from thecomputer, the juke box system allocates the target device of the otherstorage system, specified in the attach command, to the logical devicewhich is allocated to the first target device specified in the attachcommand.
 17. A storage system according to claim 12, further comprisingexternal storage subsystem information indicating the relationshipbetween the identification information of the logical device and thetarget devices provided in the other storage system, wherein the jukebox system changes the target device of the other storage system that isallocated to the logical device in accordance with the command from thecomputer to the command device, and updates the external storagesubsystem information in accordance with the change.